1. Field of the Invention
The present invention relates to a keyboard apparatus for electronic musical instruments such as electronic organ, electronic piano and synthesizer.
2. Description of the Related
Keyboards for use in above types of electronic musical instruments include a comb-teeth type disclosed in a Japanese Patent Application, First Publication, H6-342281. This will be explained briefly with reference to FIG. 13. In this type of keyboard, a white key unit 1 is comprised by resin molding all of the following components into one unit, i.e., a plurality of key stems 2 for depression; a key support section 3 extending in the widthwise direction of the key stem 2 (i.e., transverse to the longitudinal key stems) for supporting the white key stems 2; and flexible connection sections (pivot section) 4, having the same width as the back-end width of the key stem 2, to enable each key stem to vertically swing freely about the pivot point, as shown by an arrow A in the perspective drawing.
Other white key units 1' and black key units 1" are similarly constructed, and the key support section 3 of the white key unit 1 is stacked on top of the other key support section 3' of the black key units 1' while the key support section 3" of the black key unit 1" is stacked on top of the key support section 3. These units are then firmly attached to a base section of a keyboard frame (not shown) using fasteners such as screws.
This type of keyboard apparatus is low cost, however, the lengths of the key units in some of these low cost keyboards are shorter than those in the standard keyboard. In such keyboards, because the key units are shorter, they are sufficiently restricted (stiff) against yawing of the connection section, i.e., a swing movement in the horizontal direction (shown by an arrow B in FIG. 13). Therefore, in some cases key guides to restrict the horizontal swing movement of the key unit are not provided.
However, the keyboards are generally made so that the key units are free to swing vertically in the A direction, but some resisting force is necessary to be provided in the connection section 4 to limit yawing of the key stems 2 in the B direction. Otherwise, when playing glissandos, there is a danger of the adjacent keys touching, and to avoid this phenomenon, key guides have been provided at the free-end of the key stems 2 to prevent the swaying movement of the key stems 2.
Nevertheless, the key guides are a factor in increasing the production cost. Also, the key guides must be greased to prevent noise generation by sliding action against the key units, but greasing is a problematic operation, and furthermore, if the grease is dried up, noise would be generated.
Further, smooth key depression can be hindered by intrusion of foreign particles in the spaces between the key guides and the guide sections of the guided keys.
A solution to the above-mentioned problem in the comb-teeth type keyboards has been disclosed in a Japanese Patent Application, First Publication, H7-92963.
In this keyboard, as shown in FIG. 14, the overall width dimension W of the connection section 4, connecting the key stems 2 in each key unit 1 to the key support sections 3, is wider than the width dimension "a" at the back-end of the key stem 2. When the support sections 3 of a plurality of the white and black key units are assembled to produce a keyboard apparatus, parts of the connection section 4 are stacked on top of those in the adjacent key stem (provided on the other key unit) with a small intervening space.
By making the overall width W of the connection section 4 wider than width "a" of the back-end of the key stem 2, the second moment of area of the connection section 4 in the transverse direction is increased so that horizontal swing (yawing) of the key stem 2 can be restricted without using key guides, thereby permitting production of low cost keyboard that can meet general performance expectations.
However, because such keyboards are made by stacking a number of key support sections of the key units, the vertical dimension d, shown in FIG. 15, between the upper surface of the key stem 2 and the connection section 4, is different for each key unit. In other words, because the connection section 4 of each key unit is partially stacked on top of each other, a key unit whose connection section 4 is placed below that of another key unit must have a larger vertical dimension d corresponding to the stacked thickness of the connection sections 4. The result is that even for two white key units, the dimension of d is larger for the lower key unit compared with the upper key unit.
If an elastic yawing factor is expressed as a ratio of (magnitude of the yawing force)/(displacement by yawing in the horizontal swing direction), a given force will generate a lesser degree of yawing in a section having a high yawing factor than in a section having a low yawing factor. Also, the smaller the dimension d, the larger the yawing factor of a key unit.
If it is assumed that the key unit shown in FIG. 14 is an upper key unit, the elastic yawing factor for the C-key whose back-end of the key stem 2 is connected to the transverse edge of the connection section 4 is about 140 gf/mm (gram force/mm), and the elastic yawing factor for the E-key whose back-end of the key stem 2 is connected to a transverse midpoint of the connection sections is about 170 gf/mm.
The reason for causing such differences in the elastic yawing factor is that the strain in the connection section 4 caused by yawing shows a different distribution, as shown by the curve in FIG. 14, depending on the joining location of the back-end of the key stem 2 to the connection section 4.
On the other hand, for the lower key units, the elastic yawing factor for a key which is connected to a transverse midpoint of the connection section 4, as in the E-key, is about 140 gf/mm.
Therefore, even for those keys having the same connection structure, the lower key unit has a lower elastic yawing factor compared with the upper key units. This is brought about by the difference in the dimension (distance) d between the upper surface of the key stem 2 and the connection section 4, shown in FIG. 15. That is, the elastic yawing factor is higher for a key having the connection section 4 extending nearer to the upper surface of the key stem 2 (i.e., d is smaller).
From these results, it can be understood that the elastic yawing factor drops under the following two conditions:
(1) when the back lateral surface of the key stem 2 almost coincides with the lateral surface of the connection section 4, as shown by the C-key in FIG. 14; and
(2) when the key stems are connected to the key support section in the lower unit.
When these two conditions exist together, for example, when the C-key in FIG. 14 is in the lower unit (size d in FIG. 15 is larger than that in the upper unit), the elastic yawing factor drops to about 110 gf/mm. The result is that the spread in the elastic yawing factors for the keys in the upper key unit is about 140-170 gf/mm, but the overall spread in the elastic yawing factors for all the keys, including the upper and lower units, becomes 110-170 gf/mm.
As explained above, when there is a large spread in the elastic yawing factors of the keys constituting the keyboard, the player feels inconsistency in the key-touch sense to properly express artistic expressions. Also, such an arrangement is not desirable because of the possibility of adjacent keys touching during the performance.
It is, therefore, an object of the present invention to provide a keyboard apparatus having a small degree of spread in the elastic yawing factors between the upper and lower key units for the white keys, to provide an improved sense of key-touch by increasing the yawing strength of all the keys, and furthermore to prevent the yawing motion to cause the adjacent keys to touch each other during playing.
It is another object to provide a keyboard having key spacings between the adjacent keys that can be adjusted readily, especially the spacing between the highest- note-key and the adjacent key, and that can be produced with a fewer metal molds to reduce the capital cost.
It is still another object to provide a keyboard having a plurality of keys that allows easy depression of the keys while retaining moldability of the connection section and preventing the yawing movement of the keys.
There is another problem in the currently available keyboard such that, when the key support sections of the various key units are stacked and fastened to each together, a large frictional force is generated between the beveled surface of the screw head and the key support section to leave twisting strains in the screw direction in the key support sections.
Because the present keyboard does not have key guides, twisting strain in the key support section is reflected directly in the non-uniformity in the key spacings. This is highly undesirable for a high quality appearance. In particular, non-uniformity in the white key spacing becomes far more apparent at their front ends, because of a greater longitudinal length of the white keys compared with the black keys.
Therefore, it is still another object of the present invention to provide a keyboard apparatus that does not present such a problem.
There is a further problem in the type of keyboard apparatus having a wide and multiple-stacked connection sections between the key stems and the key support section to eliminate the key guides. As shown in FIG. 16, the distances db, dw formed, respectively, between the upper surface of the black key stems 2B or white key stems 2W and the upper surface of the contact section, constitutes a moment arm length for causing rolling of the key stems 2B, 2W. The moment arm lengths are dw for the white stems 2W and db for the black stems 2B.
Rolling is a rotating motion of a key about an axis extending along the longitudinal axis passing from the free end of the key through to the connection point. As can be understood from FIG. 16, the black keys 2B have a longer moment arm than the white keys 2W (i.e., dw&lt;db).
When a glissando play is performed on the keyboard of the conventional design, key stems are subjected to forces to cause their rolling motion. When the rolling moment, given by a product of the lateral forces and the moment arm lengths (db, dw), is applied to the connection section 4, because the connection section 4 is connected to the key support section 3 flexibly to permit free vertical swinging of the key stems 2B or 2W, a large moment can cause a large amount of rolling motion. Rolling motion of the keys is not desirable for good performance. Especially, because the black keys protrude further upwards compared with the white keys, their moment arm lengths are larger and more susceptible to rolling.
Therefore, the final object of the present invention is to improve the resistance to rolling in the keyboard apparatus.